Foamed metal articles are relatively new. Only very recently have the problems of uniform density and foam reproducibility been solved. Uniformity and reproducibility are required for commercial acceptance and production. This invention contributes significantly to increasing the strength-to-weight ratios of the metal foams produced. The foamed metal articles produced have generally higher strength-to-weight ratios than foamed metal articles heretofore produced.
Foamed metals have been described previously; see for example, U.S. Pat. Nos. 2,895,819; 3,300,296; 3,297,431. In general such foams are produced by adding a gas-evolving compound to a molten metal and heating the mixture to decompose the compound causing the gas evolved to expand and foam the molten metal. After foaming, the resulting body is cooled to solidify the foamed mass forming a foamed metal solid. The gas-forming solid can be metal hydride; such as, titanium hydride, zirconium hydride, or lithium hydride (such as described in U.S. Pat. Nos. 2,983,597); or in general any metal hydride which evolves hydrogen on decomposition.
Fiber reinforced foams have also been described; see U.S. Pat. Nos. 3,707,367 and U.S. 3,773,098. However, processes described require unusual low speed mixers or expensive baffled tube mixers which are slow and expensive processes. In contrast and complete contradiction to the prior art, applicants have employed high speed mixing equipment for short times to produce fiber reinforced foamed metals with acceptable uniformity, reproducibility and increased strength.